1. Field of the Invention
The invention relates to a soil compacting device.
2. Description of the Related Art
Vibratory tampers, vibrating plates or vibrating rollers are generally used for soil compaction. Whereas tampers are displacement-excited vibratory systems with a large amplitude, vibrations in the case of vibrating plates are produced by means of force excitation. For reasons connected with the excitation of vibrations in the soil particles, guideability and to protect the operator against unwanted body vibrations, vibrating plates are often designed in such a way that they have a relatively high frequency (40 to 80 Hz) and a small amplitude of the vibrating base plate. From the category of vibrating rollers, trench rollers are generally used for soil compaction, in which vibrations are produced by rotating unbalanced weights within the facings or on the chassis forming a lower mass.
When using vibrating plates, in particular, on moist soils (what are referred to as cohesive soils with a high water content or saturated soils), such as silts and clays, that is to say fine-particle soils with little tendency toward water permeability, there is the problem that the soils can only be compacted to a limited extent by the action of vibrations. This is due to the fact that the cohesion which is often typical of cohesive soils affects the adhesion of the individual particles to one another and hence prevents repositioning of the particles. In the case of vibrating plates, the small amplitude of the vibrating base plate in conjunction with the high frequency leads to a further supersaturation of the soil with water, making the latter softer and more plastic in terms of vibration and causing its adhesive effect on the vibrating plate to increase. As a result, the vibrating plate may sink into the soft earth and no longer be capable of being moved along. In practice, this has led to vibrating plates not being used in damp weather or on saturated cohesive soils even though the soil compaction and surface quality that can be achieved by means of vibrating plates are highly regarded.
In practice, however, there is frequently the problem that, although the vibrating plates are used primarily only on non-cohesive soils, it is necessary for them at certain points to cross supersaturated cohesive soils which are likewise situated in the area to be compacted. In this case, the vibrating plates run the risk of sinking in or digging themselves in due to their natural vibration as they cross these points.
DE-B 11 68 350 has disclosed a vibration device for compacting the construction site with a vibratory plate. The vibratory plate is attached by springs to a road roller, between the front roller drum and the rear wheels. To increase the contact pressure of the vibratory plate on the ground, hydraulic cylinders are provided, these hydraulic cylinders pressing the springs and the vibratory plate against the ground and thereby increasing the spring preload. The problem described of self-propelled vibrating plates on cohesive soils does not arise with this device since the roller ensures sufficient propulsion.
Similar vehicles with attached soil compacting devices are known from DE 43 40 699 A1 and DE-A 20 46 840, where a plurality of vibratory plates or tampers are attached to a heavy travel drive.
U.S. Pat. No. 5,387,370 has disclosed an electroviscous fluid for dampers with variable damping properties, the change in damping being brought about by subjecting the electroviscous fluid to a suitable electric voltage.
U.S. Pat. No. 5,547,049 describes a construction with a magnetorheological fluid in which the damping properties of the fluid can be adjusted by varying an applied magnetic field.